Red flag with a yellow single-towered castle as high as 2/3 of the flag's height and as wide as 1/3 of the flag's length.

The flag is a banner of the arms (blazonedGules, a single-towered castle Or, gate and windows of the first). The single-towered castle (in Catalan heraldry a palau torrejat or towered palace) is the traditional canting arms (palau
sa tor meaning in old Catalan "palace [of] the tower"). Flag adopted 28th December 1998. Source for image and text: Fluvià 2001.

Some additional information, extracted from this webpage of the Statistics Institute of Catalonia (Idescat):